The present invention relates to an eduction or siphon pipe for a railway tank car, and more particularly, to such an eduction pipe which has a shape corresponding to the generally curvilinear inner wall of the railway tank car, in order that the eduction pipe can readily accommodate radial distortions of the railway tank car when in service.
Eduction or siphon pipes are used in railway tank cars for loading and unloading liquid ladings through a valve on the top of the car. Eduction pipes are typically constructed to extend downwardly from the valve at the top of the car and terminate adjacent the bottom of the car, sometimes in the vicinity of a bottom sump area.
In order to remove all or substantially all of a liquid commodity within the tank car, prior art constructions have found it desirable to locate the lower end of eduction pipe as close as possible to the bottom of the tank car, such as within a bottom sump area. If the eduction pipe terminates a given distance above the tank bottom, some of the fluid commodity will be left in the bottom of the tank car after it is unloaded. Yet, it has not been possible to locate the lower end of the eduction pipe with little or no clearance relative to the bottom of the tank car or bottom sump area, since the railway tank car, is subjected to radial distortions or deflections. Such residual lading is undesirable because not all of the lading can be offloaded and because even relatively small quantities of certain environmentally hazardous materials are difficult and expensive to dispose of in a safe manner. Forces resulting from loading and unloading the fluid commodity, the movement of the train, and coupler impacts have caused the tank shell to flex in service resulting in the above-noted radial deflection of the tanks. Such forces tend to flatten the tank shell in a generally vertical direction. As a result of these tank flattening deflections, the eduction pipe is sometimes jammed into the bottom of the tank causing buckling of the eduction pipe, causing damage to the fitting at the top of the car to which the eduction pipe is connected, and causing damage to the lining inside the tank, or to the tank shell itself. Because of the need in prior art constructions to provide at least some clearance allowance between the lower end of the eduction pipe and the bottom of the car to accommodate such tank deflections, a related and continuing problem involves the inability to remove all or substantially all of the fluid from the tank car.
In order to allow limited vertical movement of the eduction pipe while positioning the lower end of the eduction pipe as close as possible to the car bottom or bottom sump area, a variety of prior art constructions have been developed. Examples of such prior art constructions are as follows: U.S. Pat. No. 1,894,655 discloses an offset eduction pipe with its lower end positioned within a bottom sump area; U.S. Pat. No. 4,008,739 employs a drop center car construction with a diagonally positioned eduction pipe; U.S. Pat. No. 4,114,783 discloses the use of a guide seal to allow telescoping movement of an eduction pipe when subjected to tank shell deflection; U.S. Pat. No. 4,219,047 provides an elastomeric boot for a telescoping eduction pipe assembly; U.S. Pat. No. 4,220,097 discloses a continuous cradle pad and skid for protecting a bottom outlet valve incorporating a siphon sump in the cradle pad; U S. Pat. No. 4,237,928 incorporates a low profile tapered sump with a complimentary-shaped guide at the lower end of the eduction pipe; U.S. Pat. No. 4,248,261 provides an upper flexible member for the eduction pipe affording axial collapse thereof; and U.S. Pat. No. 4,513,795 includes selectively variable and automatically operable eduction pipes for different levels of fill in the car.
While certain of these prior attempts to accommodate deflection of the tank and yet to insure maximum evacuation of the tank car worked well, the resulting eduction pipe arrangements were of complicated construction, expensive, and required considerable maintenance. Most new tank cars did not utilize these prior means for accommodating deflection of the tank. As a result, despite the many efforts to eliminate or reduce deflection clearance allowance between the lower end of the eduction pipe and the bottom of the railway tank car, this problem has not been overcome.